The following description will refer particularly to mixtures comprising fats, oils and greases as are typically found in sewer waste. However, the invention is also applicable to mixtures from which it is desirable to extract or separate an organic substance from solids and/or aqueous substances.
The term “biodiesel” is used to refer to vegetable or animal fat, oil or grease derived diesel, consisting of long-chain alkyl methyl (ethyl or propyl) esters. Biodiesel is distinct from petroleum diesel (also known as petrodiesel or petroleum derived diesel), which is a specific fractional distillate of petroleum fuel oil.
Fats, oils and greases are constituents of sewer waste or sewage, and are referred to commonly as “sewer grease”. Fats are triglycerides (triesters of glycerol and any of several fatty acids), and may be either solid or liquid at room temperature. Oils are neutral, non-polar molecules with a high hydrocarbon content. Greases are semisolid lubricants which generally consist of a soap emulsified with mineral or vegetable oil. Greases can be of natural origin, and can be either vegetable or animal derived.
Fats, oils and greases gather in sewer waste and are very problematic, leading to the blockage of sewerage systems. Thus they are generally considered a problematic waste product. Nevertheless, such fats, oils and greases do contain hydrocarbons, which are a potential source of valuable products such as, for example, fuels.
Typically, however, sewer grease comprises a number of waste products and aqueous materials. For example, sewer grease contains a large amount of insoluble debris and many different chemicals. Furthermore, sewer grease is very viscous and has a relatively high melting point, which is why it causes sewerage systems to become blocked.
Fuels are required to have a certain degree of purity in order to be usable. For example, biodiesel (which can in principle be made from other hydrocarbon based materials) needs to have a certain purity or FAME (fatty acid methyl ester) value in order to be usable in engines or the like. Current legislation (EN 14214) states that in order to be suitable for use in engines, biodiesel must have a minimum ester content of 96.5%. In general, the starting material used has a large impact on the quality of the biodiesel obtained.
Therefore, due to the impure and unpredictable nature of sewer grease, it has not been practicable to use sewer grease as a source of fats, oils and greases for producing fuels such as biodiesel.
It is an object of the present invention to overcome or mitigate at least some of the problems of the prior art. A further object of the invention is to obtain a material from fats, oils and/or greases that is usable to produce further products such as, for example, fuels such as biodiesel and/or the precursors thereof.